This invention relates to a pulsationless duplex plunger pump used for a liquid chromatography, medical inspection apparatus, etc. and, more particularly, to a pulsationless duplex plunger pump and a control method thereof in which velocity control is effected so as to minimize pressure pulsation.
As shown in Japanese Laid-Open No. 57-70975, in a conventional pulsationless flow pump which is a duplex plunger pump in which two plungers are reciprocated by one cam to obtain a resultant discharge through pumping operation of each of the two plungers, there is provided a mechanism which is connected to a driving motor wherein a revolution control circuit is connected to the cam and which corrects a detected output signal of the resultant discharge pressure by reversing the sign of the signal and adding the signal reversed in sign to a signal outputted from a revolution setting circuit after passing the detected output signal through a circuit for removing a component of direct current and through an amplifier. Further, the revolution control circuit comprises the revolution setting circuit, a main amplifier, and a tachogenerator which feeds back an output of the driving motor to the main amplifier.
However, in the above-mentioned prior art, (1) the detected output signal from a pressure detector is fed back through the amplifier, so that the control should be effected before a pressure pulsation takes place, while irrespectively, the revolution control is effected actually with a phase delay by a time constant which various devices or apparatus have, whereby a pressure ripple at the starting of pressure fluctuation can not be removed: (2) although only a pressure fluctuation part is detected because the detected signal of the pressure detector is passed through the circuit for removing a component of direct current, factually and accurately, a value obtained by multiplying a signal resultant from time-differentiation of the pressure fluctuation part by a constant should be a velocity correction value of the driving motor, so that the above-mentioned prior art could not effect sufficient velocity correction.